In hybrid electric vehicles (HEV), electric vehicles (EV) and the like, assembled batteries (battery systems) configured by connecting a large number of battery cells of a secondary battery in series to each other are generally used in order to secure a desired high voltage. Conventionally, a battery management device using an integrated circuit or the like is connected for each predetermined number of battery cells in such an assembled battery in order for capacity calculation and protection management of each battery cell. The battery cells are managed by controlling each charge or discharge state of the battery cells using the battery management device.
In particular, in the case of an assembled battery in which a lithium ion battery is used as a battery cell, it is dangerous that the battery management device does not operate normally and is turned into an overcharged state since the lithium ion battery has a high energy density. In this regard, a technique in PTL 1 is known in order to enhance reliability and safety of the battery management device. PTL 1 discloses a technique in which pseudo voltage information is input to a battery state detection circuit that detects a battery state of a battery cell to diagnose whether or not the battery state detection circuit is operating normally.